Lithium ion batteries, nickel-metal hydride batteries, and other secondary batteries have become more important recently as vehicle-mounted electrical power sources, and as power sources for personal computers and portable devices. In particular, it is expected that lithium secondary batteries that are light weight and provide high energy density can be preferably used as a high-output electric power source for vehicles. One typical configuration of this type of secondary battery comprises electrodes whereon a material (electrode active material) capable of reversibly absorbing and desorbing lithium ions is retained on a conductive material (current collector). Representative examples of an electrode active material that can be used for the negative electrode (negative electrode active material) include carbon materials such as graphite and amorphous carbon. Moreover, a representative example of a current collector that can be used for the negative electrode (negative current collector) is a sheet or foil component made of copper or primarily a copper alloy.
One representative method for retaining the negative electrode active material on the negative current collector when producing a negative electrode having such a configuration involves first preparing a paste for forming the active material layer by dispersing a negative electrode active material powder and a binder in a suitable solvent, next applying the paste to a negative current collector (copper foil, etc.) to form a layer containing the negative electrode active material (negative electrode active material layer) thereon, and then drying by passing the same through a hot air dryer, etc. The binder contained in the negative electrode active material layer fulfills the role of binding together the negative electrode active material itself, as well as adhering the negative electrode active material to the current collector. Patent documents 1 to 5 can be noted as technical documents relating to this kind of binder, etc.